1. Field of the Invention
The present invention relates to a dry etching apparatus, a dry etching method and a diluted anhydrous fluoride gas generator, and more particularly, to an apparatus and a method capable of selectively cleaning a surface of a substrate and removing various unnecessary films formed on the surface of the substrate in the process of semiconductor production and a diluted anhydrous hydrogen fluoride gas generator for use therein.
2. Description of Prior Art
It is a recent trend that etching of film from the surface of substrate by gas (or vapor) phase method is carried out under the presence of moisture (i.e., H.sub.2 O) of high concentration using a mixture gas of hydrogen fluoride gas and water vapor. For example, the Japanese Patent Application laid-open under Publications Nos. Sho 56-88320 and 59-166675 (unexamined) disclose a reaction which is performed by applying hydrogen fluoride gas vaporized from hydrofluoric acid. Further, the Japanese Patent Application laid-open under Publication No. Sho 62-502930 (unexamined) discloses a method in which a hydrogen fluoride gas containing moisture of high concentration is prepared by adding anhydrous hydrogen fluoride gas to water vapor.
However, in the mixture wherein hydrofluoric gas is mixed with vapor, reactivity with oxide film and other reactive films is so high that neither control of the film etching rate nor selective etching of films can be achieved. For example, it is almost impossible to etch away an unnecessary film such as native oxide film from the surface of a substrate on which thermal oxide film, CVD film, BSG film and native oxide film are formed.
Moreover, hydrogen fluoride gas mixed with moisture of high concentration brings about high corrosivity, and metals cannot be used as components of apparatus, particularly gas pipe lines through which moisture laddened hydrogen fluoride gas is supplied. Accordingly, it is necessary to employ a pipe line or a chamber made of certain polymeric resins or fluororesins, which introduce further problems in view of handling and installation. When using a gas pipe line and chamber of polymeric resin or fluororesin, there is a further disadvantage in such an aspect as joint, and it is impossible to perfectly prevent the pipe line from entrance of components of atomospheric air from outside. As a result, clean process cannot be achieved.